Do you know what tests the EC did? You really cannot definitively diagnose a liver shunt without more than blood work. They could have a general idea of course...and yes lactulose is given and usually a prescription diet. You can get that from your regular vet.
It sounds like puppy needs to be seen by an internal med specialist...and I would suggest sooner rather than later. If this is a liver shunt, only a surgical repair is going to help her. After surgery to correct a shunt, pups do usually live a long life. That is unless of course there are complications. The most important thing right now is to get her on the right food and get a work up done so that you have a definitive diagnosis and plan.
Here is a link with information about shunts:
http://www.vet.utk.edu/clinical/sacs/shunt/faq.php